The present invention relates, in general, to force indicators, and in particular, to a new and useful weight bearing indicator which is purely mechanical and simple yet provides an unambiguous message to a person wearing the indicator that a set amount of force between the person""s foot and the ground has been exceeded.
Following orthopedic surgery or injury to the lower extremities, patients are encouraged to exercise but are warned not to exert more than a certain limited amount of force on the injured lower extremity.
As a result, most patients do not apply any weight or apply insufficient weight to the injured lower extremity in fear of causing further damage. The application of weight is necessary, however, for proper recovery and not applying any weight is almost as detrimental as applying too much weight. A survey was conducted at Albany Medical College (Albany, N.Y.) involving over 100 patients. The patients indicated that often no weight was applied to the injured foot.
Electrical and electronic devices are known which sense the force applied to a foot and provide a signal to the wearer. See, for example, U.S. Pat. No. 5,408,873 which discloses a foot force sensor and U.S. Pat. No. 5,357,696 which discloses a device for measuring force applied to a wearer""s foot. The following additional patents, listed by patent number and title, are also relevant:
An electronic weight bearing alarm is also available under the trademark PEDALERT from Sammons Preston. This device monitors the amount of weight a patient places on his or her lower limb through an advanced membrane sensor. An audible beep warning is generated when the weight limit is exceeded.
The need remains for a simple mechanical device which produces-an unmistakable feedback signal to only the patient which is preferably mechanical, but which may also include an audible sound, and which can be in the shoe.
An object of the present invention is to provide a simple mechanical device which produces a tactile and in one embodiment, a tactile and audible feedback signal applied directly to the foot of the patient who wears the device in his or her shoe, sandle or other foot covering.
The device of the present invention resets automatically and requires no power source and thus is non-electric. Accordingly, there are no batteries to run down and no recharge required to maintain the usefulness of the invention for long periods of time.
A patient recovering from lower extremity injuries, surgery or other conditions such as a neurological patients, athletes and the like, simply inserts the device of the present invention into his or her shoe, under a particular area of the foot depending on the embodiment of the invention, and wears the shoe in a normal fashion. The present invention can also be incorporated into an orthotic device or cast worn by the patient on their foot.
The invention is a purely mechanical device which senses, in one embodiment, and reacts to, in another embodiment how much weight is being applied through it, that is, between the bottom of the patient""s foot and the ground, and indicates to the patient when this level is above a pre-selected value, e.g., the maximum weight permitted at the particular stage of the patient""s recovery.
According to one embodiment of the invention, a pressurized chamber is used in the device which produces a momentary tactile indication to the bottom of the wearer""s foot when the device receives more than a preselected amount of force. According to another embodiment, a so-called snap-through buckling device produces the tactile and in this case, also an audible indication in the form of a click sound.
All embodiments of the invention are reusable and automatically reset. In this way, the patient is provided with ongoing feedback on the amount of force he or she may apply to the injured area. If the set force is exceeded, the tactile sensation (and audible feedback with one embodiment) will be felt (and heard) and the patient will know to apply less force on the next step. The ability of the device to reset instantly is also essential so that the patient""s normal activities are not interrupted and the patient is also encouraged to apply as much force as possible to advance healing, without exceeding the force on a regular basis. In effect, the patient learns how much force to apply. According to the invention, the device can be configured to provide indications at different loads so that the patient can be permitted to exert higher force as the healing process continues. This is achieved simply by switching components (spring disk, coil spring or reaction plate) in each embodiment of the present invention to allow succeeding increased force limits.
Another advantage of the invention is that the feedback signal, including the audible sound, is perceptible, generally only by the patient so that no attention is drawn to the patient or the patient""s condition.
In addition to its therapeutic value, the present invention is also a simple device for use in athletics, physical therapy, gait analysis and the like, wherever a set force limit is desirable or not desirable for applying between a part of the body and another surface.
Thus, a still further object of the present invention is to provide a mechanical weight bearing indicator for producing a signal to a user when the user applies more than a selected amount of weight between an extremity of the use and a surface, comprising a reaction plate adapted to establish a frame of reference with the surface; an actuator plate mounted for movement to said reaction plate and adapted to receive weight from the user""s extremity; and purely mechanical indicator means operatively connected to said actuator plate for generating a tactile signal directly to the extremity when more than the selected amount of weight is applied to said reaction plate by the extremity.
A still further object of the present invention is to provide a mechanical weight bearing indicator which is simple in design, rugged in construction and economical to manufacture.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.